For many decades, half duplex two-way radio networks have provided reliable and convenient communications using limited shared radio resources. For example, “walkie-talkie” and citizens band (CB) radio networks have enabled users to maintain direct communication channels with other users over extended periods of time. The push-to-talk (PTT) and “instant on” features of half duplex radio devices provide desirable modes of wireless communication for users such as truckers, construction and industrial site personnel, military personnel, taxi dispatchers, police and fire personnel and numerous others. Many modern communication systems designed for public safety use group communications, which allow two or more participants to exchange voice, video, and other data. A floor control mechanism then dictates which device in the network is permitted to source media at a given time.
The Telecommunications Industry Association (TIA) Project 25 (P25) concerns a set of standards for digital radio communications for use by various emergency response teams. P25 was established to address the need for common digital public safety radio communications standards, including PTT communications standards. The P25 suite of standards involves digital land mobile radio (LMR) services commonly used by police and fire departments, and other public safety organizations. The P25 standards define numerous internet protocol (IP) interfaces. One such P25 interface, ISSI, supports interoperability between P25 systems. The ISSI for PTT was published by the TIA in the TIA-102.BACA-A documents. The ISSI provides network connectivity between P25 networks and enables network administrators to connect to other local, regional, state, or federal networks. A radio frequency subsystem (RFSS) contains a PTT server which is used during a P25 PTT session, and the ISSI enables communications between PTT servers in different RFSSs.
Referring to FIG. 1, a network diagram illustrates elements of a wireless communication network 100 including a hosted ISSI “wheel and spoke” architecture, according to the prior art. The network 100 includes P25 radios 105-n that are in radio frequency (RF) communication with corresponding “home” RF subsystems 110-n. For example, the P25 radio 105-1 communicates over a common air interface with its home RFSS 110-1. Multiple P25 radios 105-n can be registered with a RFSS 110-n. Each RFSS 110-n is then operatively coupled via an IP network 115 to a simple SIP proxy 120. The SIP proxy 120 does not have a wide area communications network (WACN) or System Identifier (ID) assigned to it directly and the simple SIP proxy 120 merely routes data packets (including voice data and control messaging) between the RFSSs 110-n. Thus, for example, if the RFSS1 110-1 seeks to send a message to both the RFSS2 110-2 and the RFSS3 110-3, the RFSS1 110-1 must send two messages explicitly: a first message targeting the RFSS2 110-2 and a second message targeting the RFSS3 110-3.
Referring to FIG. 2, a network diagram illustrates elements of a wireless communication network 200 including an agency-based ISSI “point-to-point mesh” architecture, according to the prior art. Similar to the network 100 described above, the network 200 includes P25 radios 205-n that are in RF communication with corresponding home RFSSs 210-n. For example, the P25 radio 205-1 communicates over an air interface with RFSS 210-1. However, each RFSS 210-n is operatively coupled via an IP network 215 to another RFSS 210-n. Further, to interconnect to multiple remote RFSSs 110-n, a home RFSS 110-n generally must interface with multiple IP networks, which increases security risks for the home RFSS 110-n. 
ISSI connections between RFSSs, such as those illustrated by the lines 125 and 220 in FIGS. 1 and 2, respectively, are generally private IP connections, which use wired local area network (LAN) or wide area network (WAN) technologies, or wireless technologies. The ISSI connections are generally made across a common carrier, such as a T1 or multiprotocol label switching (MPLS) carrier.
The prior art ISSI wireless communication networks 100, 200 described above can have difficulties concerning end-user configuration complexity, security, scalability, and interoperability policy enforcement.
In addition, Terrestrial Trunked Radio (TETRA) is a standard of the European Telecommunications Standards Institute (ETSI) that, similar to Project 25, concerns digital LMR services for use primarily by police and fire departments, and other public safety organizations. TETRA is popular in many parts of Europe and Asia and has particular advantages including a long range and high spectral efficiency. Communications between independent TETRA networks can be established using an inter-system interface (ISI) that provides the required bandwidth and efficient inter-system signaling. The ISI also enables other functions such as inter-system mobility management and user authentication. These ISI wireless communication networks, however, can also experience the same difficulties as the ISSI wireless communication networks described above.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present disclosure.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.